HD 102272 - First Multiplanet System around a K giant star

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HD 102272 - First Multiplanet System around a K giant star

Post by Edasich on 12th June 2008, 11:17 am

A "freshly baked" planetary system around a K giant star

http://exoplanet.eu/star.php?st=HD+102272
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Re: HD 102272 - First Multiplanet System around a K giant star

Post by Lazarus on 12th June 2008, 8:07 pm

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Re: HD 102272 - First Multiplanet System around a K giant star

Post by Sirius_Alpha on 12th June 2008, 11:55 pm

If I've understood this right, the orbits of the two planets cross.

That can't be right, they aren't in resonance.
Is there a third, undiscovered planet? (i.e. a Mu Arae scenario)

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Re: HD 102272 - First Multiplanet System around a K giant star

Post by Lazarus on 14th June 2008, 7:19 am

I created a setup with a 1.9 solar mass star in systemic and input the parameters of the planets listed in the paper - the system destabilises very quickly.

The paper mentions that they searched for stable configurations - they are displayed in figure 3 of the paper. It is a pity the parameters for the best stable configuration were not given in a table though.
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Re: HD 102272 - First Multiplanet System around a K giant star

Post by Edasich on 14th June 2008, 8:32 am

May it just be only a mistype in the paper?
I'm sure an e=0.068 is the actual value and thus we'd have got two planets in stable orbits.
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Re: HD 102272 - First Multiplanet System around a K giant star

Post by Lazarus on 14th June 2008, 9:01 am

It doesn't look that way - both the article text and figure 3 show that the best Keplerian fit has this high eccentricity.

On the other hand, the best Newtonian fits (figure 3) seem to have the planets in the 4:1 resonance (at about 1.6 AU) and with the eccentricity of the outer planet at around 0.55.
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Re: HD 102272 - First Multiplanet System around a K giant star

Post by Edasich on 15th June 2008, 11:04 am

Yeah, but it doesn't work this way. So what?
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Re: HD 102272 - First Multiplanet System around a K giant star

Post by Sirius_Alpha on 15th June 2008, 2:20 pm

Um, I still vote for the "third planet" option, lol. The radial velocity looks a tad bit unconstrained, with what looks like what may be a little bit of residual RV signals using a two-planet model:

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Re: HD 102272 - First Multiplanet System around a K giant star

Post by Edasich on 16th June 2008, 6:23 am

Inner or outer third planetary companion?
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Re: HD 102272 - First Multiplanet System around a K giant star

Post by Lazarus on 17th June 2008, 1:15 pm

I think there's also an issue that poor sampling tends to lead to solutions with higher eccentricities (note that further measurements of the 55 Cancri and HD 154345 systems ended up showing that the long-period gas giants in these systems were actually on near-circular orbits, rather than the eccentric orbits that were initially announced based on incomplete orbital coverage).
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Re: HD 102272 - First Multiplanet System around a K giant star

Post by Edasich on 17th June 2008, 2:22 pm

I'm sure those planets lay in round orbits.
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Re: HD 102272 - First Multiplanet System around a K giant star

Post by Sirius_Alpha on 9th October 2008, 8:14 pm

A paper about it. Doesn't look terribly different from "A Planetary System Around the K0 Giant HD 102272".
http://arxiv.org/abs/0810.1710

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Re: HD 102272 - First Multiplanet System around a K giant star

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